cibuild: build with --no-cache like script/docker (closes #89)

A bare `docker build .` served the Dockerfile's check steps from the
layer cache on an unchanged tree and exited 0 without running them.
script/cibuild now computes the version on its own line and runs the
same build command as script/docker and the shared policy, --no-cache
included, so every CI build runs the checks. README.md describes
script/cibuild accordingly.

Model: opus-5-5

README.md

@@ -23,8 +23,9 @@ javascript library is planned.
 
 # Build Status
 
-CI runs via `script/cibuild` (`docker build .`), which executes `make check`
-(formatting, linting, tests). The `main` branch must always be green.
+CI runs `script/cibuild`, which builds the Docker image with `--no-cache`, so
+the formatting, lint and test steps in the `Dockerfile` run on every build. The
+`main` branch must always be green.
 
 # Entrypoints
 
@@ -56,8 +57,8 @@ provide:
   Docker lint stage, whose image has no node
 - `script/check` — run `script/test`, `script/lint`, and `script/fmt-check`
 - `script/docker` — build the Docker image tagged with the project name
-- `script/cibuild` — CI entrypoint: `docker build .` (the Dockerfile runs the
-  checks)
+- `script/cibuild` — CI entrypoint: builds the image with the same command as
+  `script/docker`, uncached, so the checks in the Dockerfile run every time
 - `script/precommit` — pre-commit checks: `go mod tidy` verification, then
   `script/check`
 - `script/install-precommit` — install the git pre-commit hook that runs

TODO.md

@@ -24,6 +24,9 @@ only thing left of the `chore/align-repo-policies` branch is the list below.
 
 # Completed Steps
 
+- 2026-10-03: `script/cibuild` builds the image with the same command as
+  `script/docker`, `--no-cache` included, so the checks in the Dockerfile run on
+  every build, also on an unchanged tree (#89)
 - 2026-10-03: `fetch` refuses any manifest path that runs through a symlink
   already in the destination directory, checked before each of its writes
   (directories, temp file, rename), so such a symlink cannot send a write

script/cibuild

@@ -1,14 +1,24 @@
 #!/bin/sh
-# script/cibuild: run the CI build. The Dockerfile runs script/check
-# (via make check), so a successful build implies all checks pass.
-# Generic: needs no adaptation. The Gitea workflow runs this on push.
+# script/cibuild: run the CI build; the Gitea workflow runs this on push.
+# It builds the image with the same command as script/docker. --no-cache
+# because the checks the final stage depends on are RUN steps, and a
+# cached one is a check that did not run.
 set -eu
 
-ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
+ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    docker build .
+    # Own line: a failing command substitution inside an argument does
+    # not trip `set -e`, so the inline form degrades silently to an
+    # empty constant. The VERSION build argument takes precedence over
+    # the version a build stage derives from the .git in the context.
+    version="$(git describe --tags --always --dirty 2>/dev/null || true)"
+    [ -n "$version" ] || version="unknown"
+    docker build --no-cache \
+        --build-arg VERSION="$version" \
+        -t "$("$SCRIPT_DIR/projectname")" .
 }
 
 main "$@"